This invention relates to a sensor for gases and/or ions which uses a light source, a detector, and a sensor layer all mounted upon a single carrier body.
It is known that certain substances are suitable for measuring the partial pressure of gases and vapors and that these substances can be arranged in a test tube. However, continuous determination of the relevant gas component is not possible with these test tubes. Although mass spectrometers permit continuous measurements, the accuracy obtainable with these expensive devices is frequently not necessary.
One known embodiment of a thin-film sensor for determining the carbon dioxide content in air contains a thin sensor layer which is arranged on a carrier. The flat side of the carrier facing the sensor layer is provided with a mirror surface. The light ray of a radiation source physically separated from the sensor layer and the carrier passes through the sensor layer, is reflected at the mirror surface of the carrier and then arrives at a photoelectric converter which is likewise physically separated from the sensor and the carrier and which may be a photo cell. The light ray therefore passes through the gas sensitive sensor layer twice, the absorptivity of which is changed by the action of the gas. The corresponding color deviation of the light ray is registered by the photo cell. See Guenther U.S. Pat. No. 3,754,867, issued August, 1973.
In a known embodiment of a gas sensor for hydrogen and hydrogen compounds, a light source such as a light-emitting diode LED is connected via a light waveguide, designed as a thin film, to a detector such as a photo diode. The light waveguide is arranged on a substrate and provided with a superficial layer of a catalytic metal such as palladium (Pd) or platinum (Pt), which is subjected to the action of the gas. The light waveguide serves as a sensor and consists of a metal oxide, for example, tungsten oxide (WO.sub.3) or molybdenum oxide (MoO.sub.3). The hydrogen protons penetrate the metal layer where they are absorbed and dissociated. The hydrogen atoms released chemically reduce the sensor layer, which thereby changes its absorptivity. To enhance the absorption, the sensor is heated. See Ito, et al. U.S. Pat. No. 4,661,320, issued Apr. 28, 1987.